1. Field of the Disclosure
This disclosure relates generally to devices, systems and methods for determining position or location of equipment used in connection with the drilling, completion and/or workover of oilfield wells.
2. Description of the Related Art
Valuable hydrocarbon deposits, such as those containing oil and gas, are often found in subterranean formations located thousands of feet below the surface of the Earth. To recover these hydrocarbon deposits, boreholes or wellbores are drilled by rotating a drill bit attached to a drilling assembly (also referred to herein as a “bottom hole assembly” or “BHA”). Such a drilling assembly is attached to the downhole end of a tubing or drill string made up of jointed rigid pipe or a flexible tubing coiled on a reel (“coiled tubing”). For directional drilling, the drilling assembly can use a steering unit to direct the drill bit along a desired wellbore trajectory.
These drilled wellbores, which can include complex three-dimensional trajectories, intersect various formations of interest. During drilling and in later completion activities, success or failure of effectively producing hydrocarbons from a given formation can hinge on precisely measuring the depth of a given formation and precisely positioning a wellbore tool at a depth corresponding to a given formation. In some instances, a hydrocarbon bearing zone can be only a meter or so in depth. Thus, the positioning of wellbore tools such as a perforating gun or a kickoff for a lateral bore must be positioned well within that one meter range.
Conventional methods of determining wellbore depth are based on the number of joints or stands making up a string in the wellbore. Because each joint has a known length, the depth is determined by tracking the number of joints added to the string. Thus, typically, a processor tracks the number of joints making up a drill string. Often, however, additional joints are continually being added to the string. These additional joints also contribute to the overall length of the drill string, and thus the depth of the drill string. Conventionally, a joint is supported by a traveling block while it is added to the drill string and then the traveling block lowers the drill string into the wellbore. Thus, the vertical distance a traveling block drops indicates how much of a newly added joint has been lowered into the wellbore and how much the depth as increased due to this newly added joint. In one conventional method, the vertical distance traveled by the traveling block is measured using a mechanical device such as a wire or cable coupled to the traveling block. The length of the wire is calibrated to the vertical distance between the traveling block and a reference point such as a rig floor. The change in the vertical distance is measured by a change in wire length as wire during pay out or winding, which then is processed to determine how much of the newly added joint adds to the measured depth of the drill string.
Conventional depth measurement systems, however, may not provide the accuracy needed to position wellbore equipment within a narrow zone of interest, e.g., within a tolerance of a half-meter. The present disclosure is directed to providing more accurate determination of wellbore depth.